Polycarbonate resin is a widely used engineering plastic due to its excellent mechanical properties, heat stability, and transparency. It is desirable or necessary for the polycarbonate resin to have good flame retardant characteristics when it is used in electric or electronic products, automobile parts, office equipment, and a variety of other applications. However, the incorporation of flame retardants into polycarbonates typically leads to compromised mechanical properties, reduced impact strength, and a lower level of heat stability.
In order to obtain flame retardant polycarbonate resin, a halogen-containing flame retardant was used in U.S. Pat. No. 4,983,658 and U.S. Pat. No. 4,883,835. However, halogen-containing flame retardants will be restricted to use due to their unfriendly effect on environment. Since a siloxane-containing polycarbonate copolymer with good flame retardancy was successfully developed by GE Plastics (see U.S. Pat. No. 6,630,525), a silicone compound was also used as flame retardant for polycarbonate from United States Patent Application 20030191245 and United States Patent Application 20040220302. Phosphoric acid esters are commonly used in polycarbonate resins (see United States Patent Applications 20020077392, 20040192814 and 20040034132). In order to compensate for the impact strength loss caused by the addition of the phosphoric acid flame retardant, the impact modifier rubber was added. The rubber includes acrylonitrile-butadiene-styrene (ABS), ethylene-propylene-diene (EPDM), ethylene-propylene rubber, etc. These rubbers greatly improve the impact strength of polycarbonate resin, but they lead to low heat stability.